Radiosensitizing oxygenation changes in murine tumors treated with VEGF-ablation therapy are measurable using oxygen enhanced-MRI (OE-MRI)

Purpose: There is a significant need for a widely available, translatable, sensitive and non-invasive imag-ing biomarker for tumor hypoxia in radiation oncology. Treatment-induced changes in tumor tissue oxy-genation can alter the sensitivity of cancer tissues to radiation, but the relative difficulty in monitoring the tumor microenvironment results in scarce clinical and research data. Oxygen-Enhanced MRI (OE-MRI) uses inhaled oxygen as a contrast agent to measure tissue oxygenation. Here we investigate the util-ity of dOE-MRI, a previously validated imaging approach employing a cycling gas challenge and indepen-dent component analysis (ICA), to detect VEGF-ablation treatment-induced changes in tumor oxygenation that result in radiosensitization.Methods: Murine squamous cell carcinoma (SCCVII) tumor-bearing mice were treated with 5 mg/kg anti-VEGF murine antibody B20 (B20-4.1.1, Genentech) 2-7 days prior to radiation treatment, tissue collection or MR imaging using a 7 T scanner. dOE-MRI scans were acquired for a total of three repeated cycles of air (2 min) and 100% oxygen (2 min) with responding voxels indicating tissue oxygenation. DCE-MRI scans were acquired using a high molecular weight (MW) contrast agent (Gd-DOTA based hyperbranched poly-gylcerol; HPG-GdF, 500 kDa) to obtain fractional plasma volume (fPV) and apparent permeability-surface area product (aPS) parameters derived from the MR concentration-time curves. Changes to the tumor microenvironment were evaluated histologically, with cryosections stained and imaged for hypoxia, DNA damage, vasculature and perfusion. Radiosensitizing effects of B20-mediated increases in oxygena-tion were evaluated by clonogenic survival assays and by staining for DNA damage marker cH2AX.Results: Tumors from mice treated with B20 exhibit changes to their vasculature that are consistent with a vascular normalization response, and result in a temporary period of reduced hypoxia. DCE-MRI using injectable contrast agent HPG-GDF measured decreased vessel permeability in treated tumors, while dOE-MRI using inhaled oxygen as a contrast agent showed greater tissue oxygenation. These treatment-induced changes to the tumor microenvironment result in significantly increased radiation sensitivity, illustrating the utility of dOE-MRI as a non-invasive biomarker of treatment response and tumor sensitivity during cancer interventions.Conclusions: VEGF-ablation therapy-mediated changes to tumor vascular function measurable using DCE-MRI techniques may be monitored using the less invasive approach of dOE-MRI, an effective biomar-ker of tissue oxygenation that can monitor treatment response and predict radiation sensitivity.& COPY; 2023 Elsevier B.V. All rights reserved. Radiotherapy and Oncology xxx (2023) xxx-xxx